"What this study shows is that there are changes already happening that wouldn't be detectable to the naked eye," said Warren Jones, Ph.D., Director of Research, Marcus Autism Center.

A group of 36 children were studied starting at 2 months old. Three years later, they found out which ones had developed autism. By six months the children with autism spent less and less time looking at the eyes.

The bigger the change, the more profound the autism was.

"The earlier we diagnose, the earlier we intervene, the better the long-term outcome," said Jones.

Previous research in Boston had used eye tracking to show that babies take emotional clues from faces.

Doctors say one early sign of autism is little or no eye contact. This technology provides a tool that might show autism in its first stages.

Doctors say discovering an autism warning sign is not the same thing as discovering a way to treat it, which is why the National Institutes of Health ended its announcement Wednesday by noting that the next step for researchers is to translate this finding into a viable tool for use in the clinic, and help expand the scope for long-term studies.